In recent years, from a view point of energy saving and downsizing, light emitting diodes (hereinafter also referred to as “LEDs”) are used as a light source for illumination. Light emitting devices using a combination of an LED and a light flux controlling member that controls the distribution of light emitted from the LED are used in place of fluorescent lamps and halogen lamps. In addition, a transmission type image display device such as a liquid crystal display device uses light emitting devices disposed in a lattice as a backlight (see, for example, PTL 1).
The light emitting device disclosed in PTL 1 includes a light emitting element and a light flux controlling member. The optical axis of the light emitting element and the central axis of the light flux controlling member are aligned with each other. The light flux controlling member includes a light incidence surface configured to allow light emitted from the light emitting element to enter the light flux controlling member, a light emission surface configured to emit, to the outside of the light flux controlling member, light entered from the light incidence surface, and a bottom surface connecting the light incidence surface and the light emission surface.
The light incidence surface is an inner surface of a recess that opens toward the bottom surface side. In the light emission surface, a center portion intersects the optical axis of the light emitting element and has a smooth protruding shape protruding toward the bottom surface side. In the region outside the center portion, the light emission surface has a smooth protruding shape protruding toward the side opposite to the bottom surface side.
Light emitted from the center of the light emitting surface of the light emitting element enters the light flux controlling member from the light incidence surface while being refracted at the light incidence surface in the direction away from the central axis. The light having entered the light flux controlling member is further refracted at the light emission surface to travel away from the central axis, and is then emitted out of the light flux controlling member. In this manner, in the light emitting device disclosed in PTL 1, light from the light emitting element that has entered the light flux controlling member is actively emitted to the outside.